In rotary knife units for cutting metal sheets into strips or severing strips into blanks, the rotary knives are disposed either on two knife shafts as shown, for example, in German Patent No. 4,005,271 or are positioned in pairs on individually shiftable holder assemblies, such as disclosed, for example, in Published International Patent Application No. WO 94/00261.
The invention relates to a knife holder unit of the second type outlined above. The holder unit has a frame which is longitudinally displaceable on guide rails and has an upper and lower part for separately supporting a respective rotary knife. The cutting edges of the rotary knives oriented towards one another define a cutting plane, and further, in practice, they define a cutting gap. For purposes relevant here, the term "cutting plane" is being used without considering the cutting gap.
The knife holder unit disclosed in International Published Patent Application WO 94/00261 has a great number of individual components, such as a central knife shaft, a centering member for the transport ring and the rotary knife, two roller bearings, a threaded shifting sleeve, slit nuts, as well as a holder which supports the shifting sleeve and which passes through the machine frame. If certain tolerance values are assigned to each individual component, a summation of the individual tolerances may result in a substantial deviation and conversely: if for the rotary knife a certain tolerance is prescribed then the individual components must have very narrow tolerance values which requires a high technological input in the manufacture. The rotary knives supported by the known holder unit are countersupported on one part of the shaft which is situated externally of its bearing whereby a substantial cantilever length is obtained which leads to risks of tilting that may adversely affect the cutting operation. For disassembling the knives, due to their overlap, first a centering component has to be removed which additionally increases the labor input for assembly and disassembly.